The overall objective of this investigation is to increase our knowledge of neonatal surgical physiology by studying the newborn and young animal's physiologic and pathophysiologic responses to life-threatening challenges. Our major effort will be directed towards the study of gram negative septicemia and endotoxemia. Two projects are proposed: (1) to determine and then compare the responses of the newborn and mature organism to gram negative endotoxemia and bacteremia and (2) to study serial changes in the pulmonary microcirculation of the newborn pig resulting from gram negative bacteremia. Two projects will deal with basic information as a guide to proper interpretation of newborn research: (1) to clarify species differences between the puppy and piglet in the first week of life and (2) to study aspects of cellular function in the fetus, newborn and adult organism.